1. Field of the Invention
A novel hexa-band antenna for mobile handsets application is proposed and analyzed in this specification. An asymmetric T-type monopole antenna with a shorting-line is designed to be operated in code-division multiple access (CDMA, 824-894 MHz), global system for mobile communications (GSM, 880-960 MHz), digital communication system (DCS, 1710-1880 MHz), personal communication system (PCS, 1850-1990 MHz), wideband code division multiple access (WCDMA, 1920-2170 MHz) and Bluetooth (2400-2484 MHz) bands.
A prototype of the proposed antenna with 50 mm in length, mm in height and 15 mm in width is fabricated and experimentally investigated. The experimental results indicate that the VSWR 2:1 bandwidths achieved were 15% and 37.6% at 900 MHz and 2100 MHz, respectively. The specific absorption rate (SAR) and hearing aid compatibility (HAC) for an input power of 24 dBm in CDMA, GSM and WCDMA bands, and an input power of 21 dBm in DCS and PCS bands all meet the SAR limit of 1.6 mW/g. The current distributions on the handset body (ground-plane) as well as on the antenna element are also studied. The capability of the proposed antenna is evidenced by mitigating the degradation of antenna radiated efficiency due to human head effect and reducing SAR and HAC value. Experimental results are shown to verify the validity of theoretical work.
2. Description of the Related Art
Wireless communications continue to enjoy exponential growth in the cellular telephony, wireless Internet, and wireless home networking arenas. In order to roam worldwide, the operation bands of major wireless services, such as code-division multiple access (CDMA), global system for mobile communications (GSM), digital communication system (DCS), personal communication system (PCS), wideband code division multiple access (WCDMA) and Bluetooth should be simultaneously considered (refer to “Ramiro and Chaouki: ‘Wireless communications and networking: An overview’, IEEE Antennas Propag. Mag. (USA), vol. 44, pp. 185-193, February, 2002”).
Downsizing the handset unit, which has seen remarkable progress in recent years, requires the size reduction of the antenna element also. However, as a small antenna element is used, the utilization of the handset body is beneficial to enhance antenna performance of the handset, because the handset body is usually larger than the antenna element. Therefore, the overall effective antenna dimensions augment dramatically.
As a consequence, the corresponding gain and the bandwidth of the antenna system are increased (refer to “Chih-Hua Chang and Kin-Lu Wong: ‘Printed λ/8-PIFA for Penta-Band WWAN Operation in the Mobile Phone’, IEEE Antennas Propag., vol. 57, pp. 1373-1381, May, 2009”; “M. Z. Azad and M. Ali: ‘A Miniaturized Hilbert PIFA for Dual-band Mobile Wireless Applications’, IEEE Antennas Wireless Propag. Lett., vol. 4, pp. 59-62, 2005”;” Y. S. Shin, B. N. Kim, W. I. Kwak and S. O. Park: ‘GSM/DCS/IMT-2000 triple-band built in antenna for wireless terminals’, IEEE Antenna Wireless Propag. Lett., vol. 3, no. 1, pp. 104-107, December, 2004”; “J. D. Kraus and R. J. Marchefka, ‘Antennas’, Mc Graw-Hill, Third Edition, pp. 804-805, 2002”; “K.-L. Wong, G Y. Lee and T.-W. Chiou: ‘A low-profile planar monopole antenna for multiband operation of mobile handsets’, IEEE Antennas Propag., vol. 51, no. 1, pp. 121-125, January, 2003”; “Z. Li and Y. Rahmat-Samii: ‘Optimization of PIFA-IFA Combination in Handset Antenna Design’, IEEE Antennas Propag., vol. 53, pp. 1770-1777, May, 2005”; “P. Vainikainen, J. Ollikainen, O. Kivekäs, and I. Kelander, “Resonator-Based Analysis of the Combination of Mobile Handset Antenna and Chassis,” IEEE Transactions on Antennas and Propagation, vol. 50, no. 10, pp. 1433-1444, October, 2002”; “A. Cabedo, J. Anguera, C. Picher, M. Ribó, C. Puente, “Multi-Band Handset Antenna Combining a PIFA, Slots, and Ground Plane Modes”, IEEE Transactions on Antennas and Propagation, vol. 57, no. 9, pp. 2526-2533, September, 2009”; “R. Hossa, A. Byndas, and M. E. Bialkowski, “Improvement of Compact Terminal Antenna Performance by Incorporating Open-End Slots in Ground Plane”, IEEE Microwave and Wireless Components Letters, vol. 14, no. 6, June, 2004”; “J. Anguera, I. Sanz, A. Sanz, A. Condes, D. Gala, C. Puente, and J. Soler, “Enhancing the performance of handset antennas by means of groundplane design”, IEEE International Workshop on Antenna Technology: Small Antennas and Novel Metamaterials (iWAT 2006). New York, USA, March, 2006”; and “C. Picher, J. Anguera, A. Cabedo, C. Puente, S. Kahng, “Multiband handset antenna using slots on the ground plane: considerations to facilitate the integration of the feeding transmission line”, Progress In Electromagnetics Research C, vol. 7, pp. 95-109, 2009”).
While the use of the handset body as a part of the radiator is advantageous, it also caused disadvantage at the same time in practical operation. The antenna performance in terms of gain and input impedance varies due to the influence of the human head and hand.
Currently, a handset is normally equipped with PIFA for multi-frequency applications. However, PIFA is an unbalanced antenna having an incomplete radiation pattern. Due to noise interference, a handset of this design cannot reduce SAR (Specific Absorption Rate) and HAC (Hearing Aid Compatibility).
Previous studies (refer to “H. Morishita, H. Furuuchi and K. Fujimoto, “Performance of balanced-Fed antenna system for handsets in the vicinity of a human head or hand,” IEE Proc.—Microw. Antennas Propagat., vol. 149, pp. 85-91, 2002”; “J. J. Arenas, J. Anguera, C. Puente, “Balanced and single-ended handset antennas: free space and human loading comparison”, Microwave and Optical Technology Letters, vol. 51, no. 9, pp. 2248-2254, September, 2009”; “Yongho Kim, Hisashi Morishita, Yoshio Koyanagi and Kyohei Fujimoto: ‘A Folded Antenna System for Handset Developed and Based on the Advanced Design Concept’, IEICE Trans. Commun., vol. E84-B, pp. 2468-2475, September, 2001”) presented an antenna system having a balanced structure is effective in reducing the body effect of the handset antenna systems.